1. Field of the Invention
The invention concerns a loom having a reed which includes a plurality of blades forming a guide duct for a weft thread, and an optical weft detector containing a light emitter and a light detector for picking up light reflected from the weft thread.
2. Description of the Related Art
A loom having a reed which includes a plurality of blades forming a guide duct for a weft thread, and also an optical weft detector, is disclosed in U.S. Pat. No. 4,738,284. The light emitter and light detector of the weft detector are mounted in the vicinity of the open side of the substantially U-shaped guide duct. They are affixed to the batten and have a needle-like shape similar to that of accessory blow nozzles, so that they are able to enter the shed jointly with the batten. In this design, the light from the emitter is reflected not only by a weft thread passing through the duct but by the blades forming the guide duct. As a result, it is difficult to detect the incoming weft thread because the amount of light picked up by the light detector also depends on the soiling of the guide duct, and it is especially difficult to detect a weft thread which does not reflect a large amount of light.
Optical weft detectors are also used in the looms disclosed in U.S. Pat. No. 4,716,942, and European patent documents A 137,380 and A 290,706. In these looms, a light emitter and a light detector are mounted on the side of the reed which faces away from the guide duct, outside the blades and offset in height. Light deflecting components such as mirrors or prisms are mounted between the blades to deflect the light beam from the light emitter to the light detector, and the presence of a weft thread is determined when the light beams are interrupted. Such a weft detector suffers from the drawback that thin weft threads can be detected only with great difficulty. Furthermore, this design is disadvantageous in that the light deflecting means are mounted between the blades of the reed and therefore may damage the reed, and also in that it is cumbersome to weave narrow or wide cloths on the same loom because the light deflecting means must be reassembled each time the width is changed. Furthermore, there is a danger that, in the case of air jet looms, these light guides will interfere with the air flow in the guide duct and may lead to weaving defects.